Why Choose Black Oxide?
Black oxide coating is a chemical transformation that offers numerous advantages over traditional electroplating processes. It is commonly used on products such as drill bits, pocket knives, and cutting accessories. This type of cladding can be applied to a wide range of materials including steel, stainless steel, aluminum, cast iron, copper, brass, bronze, zinc, and more.
Black Oxide Coating in a Nutshell
Black oxide coatings, also known as magnetite or Fe3O4, come in various forms and are referred to by different names such as blackening or black passivation. Unlike powder coating or titanium coating, black oxide coating involves a chemical conversion process that creates a black iron oxide coating on ferrous metal surfaces. This process occurs through a chemical reaction between the iron on the surface of the metal and a black oxide solution consisting of oxidizing salts.
Manufacturers often go beyond the black oxide coating process and employ additional methods to enhance the metal’s corrosion and wear resistance.
Creating the Coating
Unlike electroplating, the black oxide coating is directly created on the material using a chemical conversion process. The black oxide solution contains an oxidizing agent that reacts with the iron in the steel, resulting in a coating on the surface.
For blades, manufacturers apply the coating before adding the final edge, revealing the silver edge on the brand new blade. In the case of drill bits, the ends are immersed in a chemical bath, making the coating visible on the cutting edge. Knifemakers, for example, sharpen edges after applying the black oxide coating process.
Benefits of Black Oxide Coating
Black oxide coating offers several benefits that make it a preferred choice in many applications. While more expensive coatings exist, black oxide provides a cost-effective way to improve steel compared to other options. Two key advantages of black oxide coating are corrosion resistance and reduced friction. Although these improvements are relatively minor, they elevate the performance of the product over bare steel.
Moreover, black oxide coatings do not add significant thickness to the steel they are applied to. This property is especially beneficial for precision tools like drills, as even a 5 to 10 millionths of an inch coating helps maintain sharpness.
The black oxide coating also provides a visually appealing tactical look to the product. It has the sheen of raw steel, resulting in a shiny or non-reflective matte finish.
In addition to corrosion resistance and reduced friction, black oxide coating offers several other advantages:
- Improved lubrication between components
- Anti-wear surface
- Better adhesion to paint and other finishes
- Minimal impact on conductivity
- Does not increase brittleness
- No extra fumes when welding
The limitations of any coating primarily stem from its properties rather than its penetration throughout the steel mixture. Worn areas of the steel will lose the benefits provided by the black oxide coating.
Applying Black Oxide Coating: Hot or Cold Process
Black oxide can be formed through hot or cold processes. Thermal processes, carried out at around 285°F, offer better corrosion and scratch resistance. These processes meet automotive and military standards.
In contrast, the cold process does not create a true oxide but leaves a softer coating that can be scraped off with a coin. For products like drill bits, if the areas that come into contact with the material are cold oxidized, the coating may wear off relatively quickly.
Post-Treatment of Black Oxide Coatings
To further protect the black oxide coating, manufacturers may apply clear wax or acrylic. Alternatively, they often use oil as a post-treatment. When done correctly, a thick film of oil can be left on the part, while still retaining a dry-to-the-touch surface. Light water-soluble oils or acrylic and wax treatments are commonly employed in this process.
The next time you pick up a knife or drill with a black oxide coating, you’ll have a deeper understanding of how these tools and accessories are made. If you have any additional information to share, feel free to leave it in the comments below.